Parkinson's disease is a common neurodegenerative syndrome characterized by loss of dopaminergic neurons in the substantia nigra, formation of filamentous intraneuronal inclusions (Lewy bodies), and an extra pyramidal movement disorder. Although several genes involved in familial Parkinson's disease have recently been identified, we still know very little about the molecular and biochemical events mediating neuronal dysfunction and death of dopaminergic neurons. To enable a comprehensive genetic analysis of Parkinson's disease, we have developed a Drosophila melanogaster model of the disorder. Expression of human a-synuclein in transgenic flies replicates the three cardinal manifestations of the human disease: adult-onset loss of dopaminergic neurons, filamentous intraneuronal inclusions containing a-synuclein, and progressive locomotor dysfunction. We now propose to exploit the genetic potential of the system by generating second site suppressors and enhancers of a-synuclein mediated neurodegeneration. A robust and titratable retinal phenotype suitable for genetic modification has been defined. Existing collections of well-defined mutant chromosomes will he assayed for their ability to modify the retinal phenotype. De novo mutations will also be generated and tested. Mutations that modify the retinal phenotype will be tested for their ability to alter dopaminergic neurodegeneration and inclusion formation. Modifiers of neurodegeneration and inclusion formation will be characterized molecularly. Mammalian homologues of these Drosophila modifiers will he human disease gene candidates and likely components of mammalian neurodegenerative pathways. We will also test the role of the ubiquitin/proteosome system, chaperones, and apoptosis in dopaminergic neurodegeneration using genetic methods. The role of the ubiquitin system and heat shock proteins will also be tested by looking for the presence of these proteins in Drosophila asynuclein aggregates. Ubiquitin co-localization studies will further address the relevance of the Drosophila system to human disease, because ubiquitination is a pervasive feature of human Lewy bodies. We can abolish inclusion formation in a-synuclein transgenic flies, and will determine if inclusions are required for neurotoxicity.